Transmitting two television signals through one channel

Abstract

Two input pictures are each compressed horizontally, one to three-quarters width, the other to one-quarter width, and combined side-by-side to form a single picture suitable for transmission over a standard link. The two signals are interchanged on alternate fields. Bandwidth limiting in the transmission link results in the signal compressed to one-quarter width having a final bandwidth one-third that of the other signal. This applies to each picture on alternate fields. A one-field delay repeats the high-frequencies from the field having wider bandwidth on the subsequent field, so that fine detail will be present on both fields. Lower bandwidth information is separately transmitted every field preserving vertical detail and the reproduction of motion at field rate. At the receiving end, the pictures are separated and expanded to normal width.

What is claimed and desired to be secured by Letters Patent of the United States is: 
     
       1. Apparatus for the transmission of two independent television signals through a transmission system designed for the transmission of a single television signal, comprising: a. first compression means for compressing the width of a first independent television image to produce an image of a first width being less than the width of the image supplied as input to said first compression means and greater than one-half of the width of said image supplied as input to said first compression means,   b. second compression means for compressing the width of a second independent television image to produce an image of a second width being less than half of the width of the image supplied as input to said second compression means, the sum of said first width and said second width being within the maximum width of image capable of being transmitted by said transmission system designed for the transmission of a single television image,   c. combining means for combining said image of a first width and said image of a second width to form a combined image, said combining means including means for horizontally positioning said image of a first width and separate means for horizontally positioning said image of a second width to be separated from, and horizontally adjacent to, said image of a first width,   d. means for separating said image of a first width and said image of a second width from said combined image,   e. first expansion means for expanding the width of said image of a first width to produce a first expanded image of normal width, and   f. second expansion means for expanding the width of said image of a second width to produce a second expanded image of normal width.   
     
     
       2. Apparatus as recited in claim 1 including switching means for alternately switching two television signals between the inputs of said first compression means and said second compression means and between the inputs of said first expansion means and said second expansion means, comprising: a. first switching means having a first condition of supplying a first television signal to said first compression means together with supplying a second television signal to said second compression means, and having a second condition of supplying said first television signal to said second compression means together with supplying said second television signal to said first compression means, said first switching means alternating between said first condition and said second condition at a predetermined rate, and being in said first condition and said second condition for equal times,   b. second switching means having a first condition of supplying the signal representing said first expanded image to a first output together with supplying the signal representing said second expanded image to a second output and having a second condition of supplying said signal representing said first expanded image to said second output together with supplying said signal representing said second expanded image to said first output, said second switching means alternating between said first condition and said second condition at a rate equal to the rate of alternation of said first switching means, and being in said first condition and said second condition for equal times, and   c. means for synchronization of the alternations of said second switching means with the alternations of said first switching means, whereby said first television signal always appears at said first output and said second television signal always appears at said second output, each signal alternately being passed through said first compression means and said first expansion means, and through said second compression means and said second expansion means.   
     
     
       3. Apparatus as recited in claim 2 including frequency-separating means for separating those frequency components of each television signal which are present when said signal passes through said first compression means and said first expansion means but which are excluded when said signal passes through said second compression means and said second expansion means and means for repeating said frequency components, separately for each television signal, when said signal passes through said second compression means and second expansion means, comprising: a. means for delaying the output of said first expansion means by a time delay equal to one-half the period of a complete cycle of alternation of said first switching means and said second switching means, being equal to the time duration of said first condition and to that of said second condition of said first switching means and said second switching means, to produce a delayed version of the output of said first expansion means,   b. means for separating said frequency components from said delayed version of the output of said first expansion means, to produce a high-frequency signal, and   c. means for adding said high-frequency signal to said signal representing said second expanded image prior to said second switching means, whereby the high-frequency components of said first television signal having passed through said first compression and first expansion means, are delayed and added to said first television signal, following said second expansion means, at the times of passage of said first television signal through said second compression and second expansion means, and likewise the high-frequency components of said second television signal having passed through said first compression and first expansion means are delayed and added to said second television signal, following said second expansion means, at the times of passage of said second television signal through said second compression and second expansion means.   
     
     
       4. Apparatus as recited in claim 2 having the duration of said first condition and of said second condition of said first switching means and of said second switching means separately equal to the time interval in said first television signal corresponding to the height of said first independent television image, said time interval being known as one field period, and being equal to the time interval in said second television signal corresponding to the height of said second independent television image, whereby each of said first television signal and said second television signal passes through said first compression means and said first expansion means for one field period and through said second compression means and said second expansion means for the succeeding field period.